1. Field of Endeavor
The present disclosure relates to a rotor core of a BLDC motor.
2. Background
This section provides background information related to the present disclosure which is not necessarily prior art.
In general, a rotor of a BLDC (Brushless direct current) motor is formed by press-fitting a shaft into a rotor core formed by being stacked with thin rotor core members. At this time, a surface of the shaft is performed with a surface treatment using mechanical means, e.g., knurling or skiving to inhibit the stacked rotor core and the shaft from idling. Once the shaft is surface-treated with knurling or skiving, press-fit force, pull-off force and resistance to rotational force are determined by interference between the surface treatment and a shaft hole of the rotor core.
Meantime, in case of the rotor core formed by stacking a plurality of disk-shaped rotor core members, a single rotor core having a predetermined height may be formed to be press-fitted into a skived shaft. In a case where a rotor core with more than a predetermined length is used, the rotor core is modularized at each predetermined height for easy press-fitting process, and sequentially press-fitted.
However, in case of sequential press-fitting of rotor cores, the skived surface of the shaft may be damaged in the press-fitting process of a first rotor core module, a sufficient interference cannot be reacted on second and third rotor core modules as calculated in design, and coherence between the rotor core and the shaft is not sufficiently formed to cause the shaft and the core to idle during rotation of rotor, whereby accurate power transmission and control cannot be realized.
Furthermore, in a case a tolerance between the shaft and the rotor core module is narrowly formed to inhibit from idling, an excessive stress may be generated on the shaft and the rotor core modules to generate defects such as a broken shaft, a twisted rotor core module and/or a bent deformed shaft, and in a case a magnet is installed inside the rotor core module, a magnet insertion hole for inserting the magnet may be deformed to cause a difficulty in assembling process.
Still furthermore, in case of surface treatment by skiving that is frequently used for general press-fitting process, there is a difficulty in maintaining a constant assembly performance due to thermal shrinkage/expansion, and the skew type press-fitting process twistingly arranging a plurality of rotor core members each at a predetermined angle also creates a cumbersomeness that needs adjustment of assembly angle using a jig.
It is, therefore, desirable to overcome the above problems and others by providing an improved rotor core of a motor.